In intelligent transport systems (ITSs), an electronic toll collection system (ETC (trade name), also referred to as an “automatic toll collection system”) is widely applied as a system configured to automatically collect the tolls in toll roads. The electronic toll collection system allows the tolls of toll roads to be collected by means of dedicated short-range radio communications between onboard units installed in vehicles and roadside antennas (dedicated short-range communication antennas) installed in tollgates.
In a case where a particular roadside antenna communicates with a particular onboard unit, the particular roadside antenna may have irrelevant communications with a non-target vehicle that is outside the dedicated short-range communication region defined for the valid dedicated short-range radio communications (hereinafter, such irrelevant communication(s) are referred to as “erroneous communication(s)”). For example, the reflection of the electromagnetic waves by the structure such as the ceiling of the tollgate may cause erroneous communications to be established between the roadside antenna with the onboard unit on a different vehicle that follows the vehicle in the dedicated short-range communication region (the target vehicle for the valid communications).
A technique to address such as problem is use of an electromagnetic wave absorbing panel installed in the structure on the road (see, for example, Patent Document 1).